Global distributions and trends of atmospheric ammonia (NH<sub>3</sub>) from IASI satellite observations

Abstract

Ammonia (NH₃) emissions in the atmosphere have strongly increased in the past decades, largely because of the intensive livestock production and use of fertilizers. As a short-lived species, NH₃ is highly variable in the atmosphere and its concentration is generally small, except in and close to local source areas. While ground-based measurements are possible, they are challenging and sparse. Advanced infrared sounders in orbit have recently demonstrated their capability to measure NH₃, offering a new tool to refine global and regional budgets. In this paper we describe an improved retrieval scheme of NH₃ total columns from the measurements of the Infrared Atmospheric Sounding Interferometer (IASI). It exploits the hyperspectral character of this instrument by using an extended spectral range (800–1200 cm⁻¹) where NH₃ is optically active. This scheme consists of the calculation of a dimensionless spectral index from the IASI level1C radiances, which is subsequently converted to a total NH₃ column using look-up-tables built from forward radiative transfer model simulations. We show how to retrieve the NH₃ total columns from IASI quasi-globally and twice daily, above both land and sea, without large computational resources and with an improved detection limit. The retrieval also provides error characterization on the retrieved columns. Five years of IASI measurements (1 November 2007 to 31 October 2012) have been processed to acquire the first global and multiple-year dataset of NH₃ total columns, which are evaluated and compared to similar products from other retrieval methods. Spatial distributions from the five years dataset are provided and analyzed at global and regional scales. We show in particular the ability of this method to identify smaller emission sources than those reported previously, as well as transport patterns above sea. The five year time series is further examined in terms of seasonality and inter-annual variability (in particular as a function of fire activity) separately for the Northern and Southern Hemispheres

First simultaneous space measurements of atmospheric pollutants in the boundary layer from IASI: A case study in the North China Plain

“…As shown in Figure c, thermal contrast is mainly negative, which means that boundary layer species emit more radiation than they absorb, giving rise to emission signatures in the observed spectra. Observing these for pollutants such as SO 2 or NH 3 implies the presence of enhanced loadings of these species in a boundary layer with temperature inversion or large thermal contrasts [ Clarisse et al ., ; Bauduin et al ., ; Van Damme et al ., ]. Current studies have shown that the IASI measurement of anthropogenic SO 2 in the PBL is facilitated when a combination of persisting high pollution with high negative thermal contrast and low surface humidity occurs, such as, e.g., over Norilsk (Siberia) throughout wintertime [ Bauduin et al ., ].…”

“…[] for SO 2 , and Van Damme et al . [] for NH 3 . Note that fog formation is quite common over the BTH area at this time of the year and can have an impact on the retrievals.…”

“…As shown by Van Damme et al . [], errors associated with NH 3 total columns can be high during the night (mostly above 75%) when surface sensitivity is reduced. However, during this pollution event, errors in the range of 60–75% are found within the NH 3 plumes, which is associated with the presence of temperature inversions in the PBL favoring a higher sensitivity toward the surface.…”

“…For SO 2 , the method follows the OEM development made in Carboni et al [2012], which allows better sensitivity due to the use of a wide spectral range (more information) and a dedicated spectral measurement variance-covariance matrix (more variability allowed) [see also Bauduin et al, 2013]. The NH 3 retrieval scheme consists of the calculation of a dimensionless hyperspectral index using an extended spectral range (800-1200 cm À1 ), which is subsequently converted to a total NH 3 column using look-up tables built from forward radiative transfer model simulations [Van Damme et al, 2013]. We refer to other studies for a full description of the retrieval details, namely, Hurtmans et al [2012] for CO, Bauduin et al [2013] for SO 2 , and Van Damme et al…”

The Production of Ammonia by Multiheme Cytochromes c

“…Anthropogenic perturbations of the nitrogen cycle originate from production of energy and food to sustain human populations, which cause the release of reactive nitrogen compounds, principally as nitrogen oxides (NO, NO 2 ), nitrous oxide (N 2 O), nitrate, and ammonia. Human activities have more than doubled the annual production of reactive nitrogen to satisfy human needs for food, energy, fiber, and other products [34][35][36]. In consequence, the biogeochemical nitrogen cycle has become severely unbalanced in recent decades and one main reason for this fact is the anthropogenic supply of reduced nitrogen to the biosphere in the form of NH 3 /NH þ…”